The present invention relates to a method of preserving sterilized implant which contains polymeric components, and the sterilized sealed package which contains a quench liquid reducing free radical generation and oxidative degradation, an implant, and an optional leak indicator. More particularly, the present invention provides a method for producing stable implants by reducing free radical generation and oxidative degradation of implants formed from or containing ultra high molecular weight polyethylene (UHMWPE), while at the same time, permitting cross-linking of the polymer component.
Human and animal implant components generally must be sterilized before implantation. A common sterilization approach is irradiation, especially gamma irradiation. However, irradiation can adversely affect the implant component.
In particular, gamma irradiation can adversely affect orthopaedic implant components made from or including polymeric materials. Irradiated polymeric materials typically exhibit an increased oxidation rate which is thought to be due to the formation of free radicals during irradiation. Oxidation may continue during storage after sterilization is complete. Implant oxidation can result in decreased ductility, higher wear rates, and shorter functional life.
Oxidation can be reduced in some cases by sealing the implant component in an air-tight/water-tight container before sterilization and removing the implant component from the container shortly before implantation. The container is typically filled with an inert gas or is maintained under a vacuum to prevent oxidation. Likewise, an oxygen absorbent material can be placed inside the container to remove oxygen.
However, if the container seal is compromised, undetected oxygenation can occur. Another problem is that filling a container with a gas and subsequent sealing is complex. Upon sealing, the gas diffusion rate of the container limits the shelf-life of the sealed component as oxygen from the surrounding air diffuses into the container.
Hence, one problem with preserving implant components, particularly those containing polymeric materials, is limited shelf-life. Another is undetected container breach which reduces the functional life of the implant component.
The present invention provides a method of preserving polymeric materials after sterilization and before implantation such that free radical generation are minimized, and the packaged containers in which the method can be carried out and stored after sterilization.
One aspect of the present invention is a method of sterilizing which reduces free radical generation and oxidative degradation of implants formed from or containing polymeric materials, permits cross-linking of the polymer component, and increases shelf-life of the sterilized implant.
Another aspect of the present invention is providing a packaged implant for sterilization with sufficient quench liquid for sterilization and to avoid formation of a dry surface on the packaged implant.
A still further aspect of the present invention is preserving an polymer containing implant by contacting the component with a free radical quenching fluid in a closed environment,and sterilizing the in the presence of radiation in the presence of the free radical quenching fluid.
A further aspect of the present invention is providing a sealed and sterilized package, e.g., an article of manufacture, which includes (i) a fluid impermeable, sealed, radiation transparent container, (ii) a free radical quenching liquid within the container, and (iii) an implant component including a polymeric material, the liquid and implant component being sealed in the sealed container.